The manufacture of radar sensors for vehicles is subject in particular to the tolerances of the used mechanical components on or in which the antennas of the radar components are mounted. This typically results in a mechanical sensor axis and a radar sensor axis that deviate from one another.
The radar sensor is assembled in the vehicle so that the radar axis is aligned at a precisely defined angle with respect to the travel axis. This may be performed in two ways in particular.
The sensor is installed on the vehicle and is in operation. This means that it is transmitting radar waves. Actual value α of the azimuth angle and the elevation angle of the radar axis in relation to the travel axis of the vehicle is ascertained from the reflected radar intensities. Deviations from the setpoint value, i.e., the angle between the radar axis and the travel axis, are corrected with the aid of adjusting means on the radar sensor holder or on the radar sensor itself. This type of adjustment may also be referred to as an active adjustment.
In particular, it is disadvantageous that a radar sensor must be in operation for the adjustment and in this respect transmits radar waves that may interfere with electrical consumers, for example.
For the second type of adjustment which may also be referred to as a passive adjustment, a mirror adhered to or vapor-deposited on the radar sensor is additionally used. At the radar sensor manufacturing plant, an angle deviation β between the radar axis and a mirror normal is ascertained and stored in the sensor. A deviation y of the mirror normal with respect to the travel axis is then measured by the vehicle manufacturer. The stored values are read out, calculated, and taken into consideration as correction factors. The radar axis is corrected to the travel axis via an adjustment.
It is disadvantageous in particular that the mirror position may change over time due to aging of the adhesive foil. In particular, the properties of the adhesive foil under the mirror change over the service life of the sensor. For example, it becomes brittle due to high temperatures or swells due to high humidity. As a result, the originally measured and stored deviations of the radar axis and the mirror normal no longer match the actual values. As a result, passive adjustment is not possible in a service case, i.e., in particular during a function test of the radar sensor.
Moreover, the reflectivity may decrease due to contamination of and/or oxidation of and/or mechanical influences on the reflective layer. A passive adjustment may not be reliably ensured in a service case.